About change of internal energy(q41)

[jack1234]

For this question:
http://tinyurl.com/3ahesh
the answer is a.

May I know how do we come to the conclusion that the net change of internal energy of the gas is zero?

 

[Pythagorean]

The energy is introduced into the system when the gas is heated up (but kept at the same volume). This energy is lost when the gas contracts freely at constant pressure and temperature from B to To.

So the energy is gained through heat (dQ) which raises the pressure, then the energy is converted to work on the system, raising the volume (pdV) but keeping the temperature the same, then the gas freely contracts, losing energy through work. (p(V2-V1)).

 

[ogb p]

I would like to clarify that the answer "a" is not a conclusion, but rather a statement of the first law of thermodynamics. This law states that the change in internal energy of a closed system is equal to the heat added to the system minus the work done by the system. In the given question, the system is a gas and it is in a closed container, meaning that there is no exchange of matter or energy with the surroundings. Therefore, according to the first law of thermodynamics, the net change in internal energy must be zero as there is no heat added or work done on the system. It is important to note that this is assuming ideal conditions, where there is no energy loss due to friction or other external factors. Any deviation from ideal conditions may result in a non-zero change in internal energy.